JP3481229B2 - Power circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a power supply circuit of a portable device operated by a battery or the like. 2. Description of the Related Art As a power supply for portable equipment, a switching power supply that can be reduced in size and weight is often used. The switching power supplies are roughly classified into two types, that is, a PWM converter that operates with a rectangular wave and a resonant converter that operates with a sine wave, when roughly classified according to the waveforms of switch voltages and currents. As a conventional technique, a PWM step-up converter will be described as an example. FIG. 6 is a block equivalent circuit diagram showing a conventional power supply circuit. In the figure, 1 is an input terminal to which a power supply such as a battery is connected, 2 is an element (hereinafter, referred to as a switch) that operates similarly to a switch that connects or disconnects the power supply and the circuit, and 3 is an input voltage. An element that operates in the same manner as a stabilizing capacitor (hereinafter, referred to as an input capacitor), 4 is an element that operates in the same manner as an inductor that stores energy (hereinafter, referred to as an inductor), and 5 performs a switching operation An element that operates in the same manner as a transistor (hereinafter, referred to as a transistor), 6 is an element that operates in the same manner as a rectifying diode (hereinafter, referred to as a diode), and 7 is a capacitor that smoothes a rectified waveform. (Hereinafter, referred to as an output capacitor), 8 is a control circuit for controlling the output voltage to be constant, and 9 is an output terminal connected to a load circuit. Next, the operation will be described by taking a case where a battery is connected as a power supply as an example. The DC voltage output from the battery is applied to the input terminal 1. The DC voltage applied to the input terminal 1 is applied to one terminal of the switch 2 and the other terminal is connected to the circuit side. When the terminals of the switch 2 are open, the power is shut off. When the terminals of the switch 2 are closed, the power is on. When the switch 2 is closed, the input direct current charges the input capacitor 3 and is simultaneously supplied to the circuit after the inductor 4.
The input capacitor 3 discharges when the load current suddenly increases, and stabilizes the input voltage against a load change. When the transistor 5 is on, the inductor 4 is excited and energy is stored in the inductor. When the transistor 5 is off, the magnetic flux of the inductor 4 is reset, and the energy stored in the inductor is released to the circuit after the diode 6. The diode 6 conducts when the potential on the cathode side is lower than the potential on the anode side, and charges the output capacitor 7. When the potential on the cathode side is higher than the potential on the anode side, such as when the transistor 5 is on, the diode 6
Shuts off. When the diode 6 is shut off, the output capacitor 7 discharges and supplies the load circuit connected to the output terminal 9. The control circuit 8 monitors the potential of the output terminal 9, compares it with a reference voltage, and controls on / off of the transistor 5 so that the output voltage is kept constant. Further, the current flowing through the transistor 5 is monitored, and ON / OFF of the transistor 5 is controlled so as not to exceed a certain current value. The control circuit 8 controls the on / off of the transistor 5 by changing a frequency with one cycle of on / off.
Alternatively, it is performed by varying the duty cycle of the ON / OFF cycle, interrupting the switching operation, or the like. Immediately after the switch 2 is turned on, the output voltage becomes 0
Since it is V, the control circuit 8 turns on the transistor 5 so as to increase the output voltage. When the switch 2 is turned on, a current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 simultaneously flow from the power supply. Due to the large current required immediately after the switch 2 is turned on, the input voltage is significantly reduced due to the internal resistance of the battery. At this time, since the input voltage is also a power source of the control circuit 8, if the input voltage drops significantly, the control circuit 8 may not operate. If the control circuit 8 does not operate with the transistor 5 turned on, the current continues to flow through the transistor 5, so that the input voltage may remain low and the output voltage may not be obtained. The above operation will be described based on a specific example. For example, the inrush current of the input capacitor 3 has a peak of 1.5
A, the case where the maximum collector current of the transistor 5 is 2 A, the minimum operating power supply voltage of the control circuit 8 is 1.8 V, the initial voltage of the battery is 3.2 V, and the internal resistance is 0.5Ω. The potential drop amount of the output from the battery when the inrush current is at a peak is (1.5A + 2A) × 0.5Ω = 1.75V. The input voltage drops by 1.75V from the initial voltage, so that 3.2V-1.75V = 1.45V. 1.45V <1.8V Therefore, the minimum operating power supply voltage of control circuit 8 of 1.8V
1.45V which is lower than that. Thus, switch 2
Immediately after turning on, when the rush current of the input capacitor 3 reaches a peak, the control circuit 8 may not operate with the transistor 5 turned on. Since the conventional power supply circuit is configured as described above, there is a possibility that a correct output voltage cannot be obtained even when the switch 2 is turned on. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. Even when a battery or the like having a large internal resistance is connected, it does not operate due to a decrease in the battery output voltage due to an inrush current or the like. It is an object of the present invention to obtain a power supply circuit that is prevented. A power supply circuit according to the present invention comprises a power supply switch for connecting or disconnecting a power supply and a circuit .
And switches, is connected to the power supply switch, accumulation and input capacitor to stabilize the input voltage change by the current supplied from the power source side is connected to the power supply switch, the energy simultaneously in parallel with the input capacitor an inductor that is provided between the output side and the ground potential of the inductor, the energy accumulated in the inductor in the on state, and the switching section you like flux of the inductor are reset in the oFF state, the A rectifying unit that rectifies the output of the inductor, an output capacitor that smoothes the rectified waveform, and the switching unit that uses the input voltage from the power supply switch as a power source so that the output voltage is constant. in the power supply circuit and a control unit for on-off control, immediately after the power supply switch to the connection state Luo to the input capacitor charges
Power supply circuit, characterized in that a behavior blocking section stops the operation of the control unit. In a power supply circuit according to an embodiment of the present invention, the operation start of the power supply circuit is delayed from the start of power supply, so that the current required at the start of power supply and the power supply circuit The required current does not flow at the same time when the operation starts, the potential drop of the input voltage decreases, and the power supply circuit does not operate. Further, since the input passing through the switch section is supplied to the control section as power after the noise is reduced through the low-pass filter, the power supply circuit does not operate. Further, since the charge storage element is provided on the power supply side of the switch section, a spare battery in which the charge is stored before the switch is turned on is formed, and the charge storage element is stored in response to a large current demand after the switch is turned on. The potential drop of the input voltage can be suppressed by the supply from the element side, and the power supply circuit does not operate. Further, since the capacity of the charge storage element on the power supply side of the switch section is increased and the capacity of the charge storage element on the load side of the switch section is reduced, the rush current due to the switching on is reduced, and the potential of the input voltage is reduced. The drop can be suppressed small, and the power supply circuit does not operate. Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment. Embodiment 1 FIG. FIG. 1 is a block equivalent circuit diagram showing a power supply circuit according to Embodiment 1 of the present invention. The operation of each block is represented by an equivalent circuit for easy understanding.
In FIG. 1, reference numeral 10 denotes an interruption circuit for interrupting the operation of the control circuit 8. The other components are the same as those shown in FIG. 6 with the same reference numerals. Next, the operation will be described. When the switch 2 is closed, the input DC current charges the input capacitor 3 and is also supplied to the circuit after the inductor 4 and the cutoff circuit 10. The shutoff circuit 10 supplies the control circuit 8 with a signal for shutting off the control circuit 8 so that the control circuit 8 does not operate for a certain time after the switch 2 is turned on. Control circuit 8
Stops the operation while the signal indicating the interruption is output from the interruption circuit 10. When the control circuit 8 stops operating, the transistor 5 is turned off. The operation of the other parts is the same as the operation of the conventional device shown in FIG. 6, and the description of the operation is omitted. When the switch 2 is turned on, the cutoff circuit 1 is turned on.
0 stops the operation of the control circuit 8. As soon as the switch 2 is turned on, charging of the input capacitor 3 is started. At this time, no current flows through the transistor 5. After a lapse of time sufficient to charge the input capacitor 3, the shutoff circuit 1
0 starts the operation of the control circuit 8. When the control circuit 8 starts operating, a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 flows. Since the input capacitor 3 is already charged, a large current such as an inrush current does not flow. A current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 do not flow from the power supply at the same time. Therefore, the input voltage does not drop significantly due to the internal resistance of the battery, and the control circuit 8 does not stop operating, so that the power supply circuit operates normally and a normal output voltage is obtained. The above operation will be described based on a specific example used in the description of the conventional example. For example, the inrush current of the input capacitor 3 is 1.5 A peak, the maximum collector current of the transistor 5 is 2 A, and the minimum operating power supply voltage of the control circuit 8 is 1.8.
V, the initial voltage of the battery is 3.2 V, and the internal resistance is 0.5Ω. The potential drop amount of the output from the battery when the inrush current is at a peak is 1.5A × 0.5Ω = 0.75V. Since the input voltage drops 0.75 V from the initial voltage, 3.2 V−0.75 V = 2.45 V. 2.45V> 1.8V Therefore, the minimum operating power supply voltage of control circuit 8 of 1.8V
2.45V, which is higher than that, and there is no problem. When the current flowing through the inductor 4 and the transistor 5 has a peak, the potential drop amount of the output from the battery is calculated as 2A × 0.5Ω = 1.0V. Since the input voltage drops 1.0 V from the initial voltage, it becomes 3.2 V-1.0 V = 2.2 V. 2.2V> 1.8V Therefore, the minimum operating power supply voltage of control circuit 8 of 1.8V
2.2V, which is higher than that, and there is no problem. Furthermore, since the input capacitor 3 is already charged when a current flows through the inductor 4 and the transistor 5, it is not necessary to supply all necessary current from the battery, and the input capacitor 3 is also supplied from the input capacitor 3, so that the current does not actually drop to this point. . By shifting the timing at which a large current flows,
Since the input voltage does not drop significantly due to the internal resistance of the battery and the control circuit 8 does not stop operating, the power supply circuit operates normally and a normal output voltage can be obtained. . FIG. 2 is a block equivalent circuit diagram showing one configuration example of the cutoff circuit 10. As shown in FIG. In the figure, 20 is a switch 2
An input terminal to which an input voltage passed is applied, 21 is a capacitor, 22 is a resistor, 23 is a reference voltage source, 24 is a comparator,
An output terminal 25 outputs a signal to the control circuit 8. FIG. 3 is a waveform chart for explaining the operation of one configuration example of the shutoff circuit 10. As shown in FIG. The operation will be described with reference to FIGS. The input voltage applied to the input terminal 20 rises when the switch 2 is turned on from off.
The capacitor 21 and the resistor 22 form a high-pass filter, and supply a differential waveform corresponding to a change component of the input voltage to one input terminal of the comparator 24. The reference voltage source 23 supplies a predetermined constant voltage to the other input terminal of the comparator 24. The comparator 24 compares the output of the high-pass filter with the reference voltage. When the output of the high-pass filter is higher than the reference voltage, the logic of the high level indicates that the output of the high-pass filter is higher than the reference voltage. When the signal is small, a logic signal that becomes a logic of a low level is output from the output terminal 25.
The shutoff circuit 10 outputs a logic signal which becomes High level during a period required for shutoff immediately after the switch 2 is turned on.
To stop the operation of the control circuit 8 for a certain period immediately after the switch 2 is turned on. Embodiment 2 FIG. FIG. 4 is a block equivalent circuit diagram showing a power supply circuit according to Embodiment 2 of the present invention.
The operation of each block is represented by an equivalent circuit for easy understanding. In FIG. 4, reference numeral 11 denotes a noise reduction circuit for reducing noise on a power supply for operating the control circuit 8. The noise reduction circuit 11 is a low-pass filter that suppresses high-frequency component noise and passes only low-frequency components. The other components are the same as those shown in FIG. 6 with the same reference numerals. Next, the operation will be described. When the switch 2 is closed, the input DC current charges the input capacitor 3 and is also supplied to the circuit after the inductor 4 and the noise reduction circuit 11. The noise reduction circuit 11 reduces the noise of the input voltage and supplies the noise to the control circuit 8 as a power supply for the control circuit 8. The operation of the other parts is the same as the operation of the conventional device shown in FIG. 6, and the description of the operation is omitted. The operation in the case where the noise reduction circuit 11 is not provided will be described focusing on noise. Since the output voltage is 0 V immediately after the switch 2 is turned on, the control circuit 8 increases the output voltage.
Turns on the transistor 5. When the switch 2 is turned on, a current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 simultaneously flow from the power supply. Due to the large current required immediately after the switch 2 is turned on, the input voltage decreases due to the internal resistance of the battery. Even if the decrease in the input voltage is still in the range in which the control circuit 8 operates, the noise component on the reduced input voltage may cause the negative peak to drop to a voltage at which the control circuit 8 does not operate. is there.
When the control circuit 8 does not operate with the transistor 5 turned on, the current continues to flow through the transistor 5, so that the input voltage may remain low irrespective of the noise component and the output voltage may not be obtained. There is a case where the drop of the input voltage is fixed by using the negative peak of the noise on the input voltage as a trigger. Next, the operation in the presence of the noise reduction circuit 11 will be described with a focus on noise. Immediately after switch 2 is turned on,
Since the output voltage is 0 V, the control circuit 8 turns on the transistor 5 so as to increase the output voltage. When the switch 2 is turned on, a current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 simultaneously flow from the power supply. Due to the large current required immediately after the switch 2 is turned on, the input voltage decreases due to the internal resistance of the battery. If the decrease width of the input voltage is still within the range in which the control circuit 8 operates, the control circuit 8 operates without being affected by the noise component. Therefore, since the control circuit 8 does not stop operating, the power supply circuit operates normally and a normal output voltage can be obtained. Embodiment 3 FIG. FIG. 5 is a block equivalent circuit diagram showing a power supply circuit according to Embodiment 3 of the present invention.
The operation of each block is represented by an equivalent circuit for easy understanding. In the figure, reference numeral 12 denotes an element (hereinafter, referred to as a power supply side capacitor) which operates in the same manner as a capacitor for stabilizing an input voltage. The other components are the same as those shown in FIG. 6 with the same reference numerals. Next, the operation will be described. The DC voltage output from the battery is applied to the input terminal 1. Input terminal 1
Is applied to one terminal of the switch 2 at the same time as charging the power supply side capacitor 12, and the other terminal is connected to the circuit side. When the terminals of the switch 2 are open, the power is shut off. When the terminals of the switch 2 are closed, the power is on. When the switch 2 is closed, the input direct current charges the input capacitor 3 and is simultaneously supplied to the circuit after the inductor 4. When the load current suddenly increases, the input capacitor 3 and the power supply-side capacitor 12 discharge to stabilize the input voltage with respect to load fluctuation. The subsequent operation is the same as the operation of the conventional device shown in FIG. 6, and the description of the operation is omitted here. Before the switch 2 is turned on, an electric charge is stored in the power supply side capacitor 12. Since the output voltage is 0 V immediately after the switch 2 is turned on, the control circuit 8 turns on the transistor 5 so as to increase the output voltage. Switch 2
Is turned on, a current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 simultaneously flow from the power supply and the power supply side capacitor 12. The large current required immediately after the switch 2 is turned on depends not only on the battery but also on the power supply side capacitor 12.
, The decrease in the input voltage affected by the internal resistance of the battery is reduced. The input voltage is controlled by the control circuit 8
However, the control circuit 8 does not stop operating due to the reduced width of the input voltage, and the power supply circuit operates normally and a normal output voltage can be obtained. Embodiment 4 FIG. 5 is a block equivalent circuit diagram showing a power supply circuit according to Embodiment 4 of the present invention.
The configuration is the same as that of the third embodiment. The power supply side capacitor 12 is a capacitor having a sufficiently larger capacitance than the input capacitor 3. For example, if the input capacitor is 20 μF
In contrast, the power supply side capacitor 12 has a capacitance ratio of about 10 times, such as 200 μF. Next, the operation will be described. The DC voltage output from the battery is applied to the input terminal 1. Input terminal 1
Is applied to one terminal of the switch 2 at the same time as charging the power supply side capacitor 12, and the other terminal is connected to the circuit side. When the terminals of the switch 2 are open, the power is shut off. When the terminals of the switch 2 are closed, the power is on. When the switch 2 is closed, the input direct current charges the input capacitor 3 and is simultaneously supplied to the circuit after the inductor 4. When the load current suddenly increases, the input capacitor 3 and the power supply-side capacitor 12 discharge to stabilize the input voltage with respect to load fluctuation. The subsequent operation is the same as the operation of the conventional device shown in FIG. 6, and the description of the operation is omitted here. Before the switch 2 is turned on, a charge is stored in the power supply side capacitor 12. Since the output voltage is 0 V immediately after the switch 2 is turned on, the control circuit 8 turns on the transistor 5 so as to increase the output voltage. Switch 2
Is turned on, a current for charging the input capacitor 3 and a current for exciting the inductor 4 flowing through the inductor 4 and the transistor 5 simultaneously flow from the power supply and the power supply side capacitor 12. The large current required immediately after the switch 2 is turned on depends on the power supply side capacitor 12 as well as the battery.
, The decrease in the input voltage affected by the internal resistance of the battery is reduced. Since the capacity of the input capacitor 3 is sufficiently smaller than the capacity of the power supply side capacitor 12, the input capacitor 3 can be charged with the electric charge stored in the power supply side capacitor 12. Therefore, the inrush current of the input capacitor 3 is reduced, and the decrease in the input voltage, which is affected by the internal resistance of the battery, is reduced.
Does not stop operating, the power supply circuit operates normally, and a normal output voltage is obtained. Since the present invention is configured as described above, it has the following effects. Since the start of the operation of the power supply circuit is delayed from the start of the supply of the power supply, the current required at the start of the power supply and the current required at the start of the operation of the power supply circuit do not flow at the same time, and the potential drop of the input voltage is reduced. The power supply circuit operates reliably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block equivalent circuit diagram showing a power supply circuit according to a first embodiment of the present invention. FIG. 2 is a block equivalent circuit diagram illustrating a configuration example of a cutoff circuit. FIG. 3 is a waveform chart for explaining the operation of one configuration example of the cutoff circuit. FIG. 4 is a block equivalent circuit diagram showing a power supply circuit according to a second embodiment of the present invention. FIG. 5 is a block equivalent circuit diagram showing a power supply circuit according to Embodiments 3 and 4 of the present invention. FIG. 6 is a block equivalent circuit diagram showing a conventional power supply circuit. [Description of Signs] 1 input terminal, 2 switch, 3 input capacitor, 4
Inductor, 5 transistor, 6 diode, 7
Output capacitor, 8 control circuit, 9 output terminal, 10
Cut-off circuit, 11 noise reduction circuit, 12 power supply side capacitor, 20 input terminal, 21 capacitor, 22 resistor, 23 reference voltage source, 24 comparator, 25 output terminal.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigehiro Matoba 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation (56) References JP-A-7-123702 (JP, A) JP-A Heisei 8-280170 (JP, A) JP-A-56-123024 (JP, A) JP-A-7-79562 (JP, A) JP-A-4-12671 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/155 H02J 1/00

Claims (1)

(57) [Claims] [Claim 1] Connect or disconnect the power supply side and the circuit side
And a power supply switch, is connected to the power supply switch, an input capacitor for stabilizing the input voltage change by the current supplied from the power source side is connected to the power supply switch, energy simultaneously in parallel with the input capacitor Provided between the output side of the inductor and the ground potential,
The energy accumulated in the inductor in the on state, and the switching unit Ru to <br/> as flux the inductor are reset in the OFF state, and a rectifying unit for rectifying an output of the inductor, the rectified waveform A power supply circuit comprising: an output capacitor for smoothing the power supply switch; and a control unit that controls on / off of the switching unit so that an output voltage is constant, using an input voltage from the power supply switch as a power supply. power supply circuit, characterized in that a behavior blocking section stops the operation of the control unit to the input capacitor charges immediately after the.